This invention relates to a method for hydroentanglement of continuously extruded essentially endless thermoplastic polymer filaments, the apparatus for carrying out the method, and the products produced thereby.
The term “hydroentanglement” refers to a process that was developed in the 1950's and earlier as a possible substitute for a conventional weaving process. In a hydroentanglement process, small, high intensity jets of water are impinged on a layer of loose fibers, with the fibers being supported on an unyielding perforated surface, such as a wire screen or perforated drum. The liquid jets cause the fibers, being relatively short and having loose ends, to become rearranged, with at least some portions of the fibers becoming tangled, wrapped, and/or knotted around each other. Depending on the nature of the support surface being used (e.g. the size, shape and pattern of openings), a variety of fabric arrangements and appearances can be produced, such as a fabric resembling a woven cloth or a lace.
The term “spunbonding” refers to a process in which a thermoplastic polymer is provided in a raw or pellet form and is melted and extruded or “spun” through a large number of small orifices to produce a bundle of continuous or essentially endless filaments. These filaments are cooled and drawn or attenuated and are deposited as a loose web onto a moving conveyor. The filaments are then partially bonded, typically by passing the web between a pair of heated rolls, with at least one of the rolls having a raised pattern to provide a bonding pattern in the fabric. Of the various processes employed to produce nonwovens, spunbonding is the most efficient, since the final fabric is made directly from the raw material on a single production line. For nonwovens made of fibers, for example, the fibers must be first produced, cut, and formed into bales. The bales of fibers are then processed and the fibers are formed into uniform webs, usually by carding, and are then bonded to make a fabric.
Hydroentangled nonwoven fabrics enjoy considerable commercial success primarily because of the variety of fiber compositions, basis weights, and surface textures and finishes which can be produced. Since the fibers in the fabric are held together by knotting or mechanical friction, however, rather than by fiber to fiber fusion or chemical adhesion, such fabrics offer relatively low tensile strength and poor elongation. In order to overcome these problems, proposals have been advanced to entangle the fibers into an already existing separate, more stable substrate, such as a preformed cloth or array of filaments, where the fibers tend to wrap around the substrate and bridge openings in the separate substrate. Such processes obviously involve the addition of a secondary fabric to the product, thereby increasing the associated effort and cost.
Another method for improving strength properties is to impregnate the fabric with adhesive, usually by dipping the fabric into an adhesive bath with subsequent drying of the fabric. In addition to adding cost and effort to the process, however, addition of an adhesive may undesirably affect other properties of the final product. For instance, treatment with an adhesive may affect the affinity of the web for a dye, or may otherwise cause a decline in aesthetic properties such as hand and drape as a result of increased stiffness.
Because of the above discussed problems associated with hydroentangled webs, the hydroentangling practice as known by those skilled in the art heretofore has been limited only to staple fibers, to pre-bonded webs, or to filaments of only an extremely small diameter. The hydroentanglement of webs of filaments that are continuous, of larger diameter, or higher denier has heretofore not been considered feasible. Conventional wisdom suggests that long, large diameter, continuous filaments would dissipate energy supplied by entangling water jets, and thereby resist entanglement. An additional factor suggesting that continuous filaments could not be sufficiently hydroentangled to form a stable, cohesive fabric is that as the filaments are continuous they do not have loose free ends required for wrapping and knotting. Yet another problem in the hydroentangling process as presently known and practiced in the industry is associated with production speed limitations. Presently known methods and apparatuses for hydroentangling filaments are not able to achieve rates of production equal to those of spunbonding filament production.
There is therefore an as yet unresolved need in the industry for a process of hydroentangling continuous filaments of relatively large denier. Also, there is a heretofore unresolved need in the industry for a hydroentangled nonwoven fabric comprised of continuous filaments of relatively large denier. Further, there is an unresolved need in the industry for an apparatus for producing a nonwoven web comprised of hydroentangled continuous filaments of relatively large denier, and for a method and apparatus for hydroentanglement capable of rates of production substantially equal to spunbonding production rates.
Objects of the Invention
It is an object of the present invention to provide a hydroentangled nonwoven fabric comprised of continuous filaments of relatively large denier.
It is a further object of the present invention to provide a process and apparatus for hydroentangling continuous filaments of relatively large denier at rates of production substantially equal to rates of spunbonding production.
It is a still further object of the invention to provide an apparatus for producing a nonwoven web comprised of hydroentangled continuous filaments of relatively large denier.